Cette thèse porte sur l’étude et le développement d’électrocatalyseurs à base d’iridium pour la réaction de dégagement de dioxygène (OER) dans les électrolyseurs à membrane échangeuse de protons. En raison de la dégradation marquée des électrocatalyseurs en conditions OER, nous nous sommes particulièrement intéressés à la recherche d’un compromis optimal entre activité catalytique et stabilité. Différents électrocatalyseurs (supportés sur noir de carbone, supportés sur oxydes métalliques dopés et non-supportés) ont été synthétisés et caractérisés par des méthodes électrochimiques et physico-chimiques, notamment par spectroscopie photoélectronique X, microscopie électronique en transmission à localisation identique et spectrométrie de masse à plasma à couplage inductif. Les électrocatalyseurs supportés sont les moins stables en conditions OER, notamment du fait de l’agglomération, la coalescence, la dissolution et le détachement des nanoparticules d’oxyde d’iridium. Ces deux derniers mécanismes de dégradation sont exacerbés par la corrosion des supports carbonés et la dissolution des éléments composant les supports oxydes métalliques dopés. Les électrocatalyseurs non-supportés offrent ainsi le meilleur compromis entre activité et stabilité. Les degrés d’oxydation Ir(III) et Ir(V) ont été identifiés comme les plus actifs pour l’OER en électrolyte acide tandis que l’oxyde Ir(IV) est le plus stable, l’espèce la moins stable étant l’iridium métallique Ir(0). La dégradation des couches catalytiques en cellule d’électrolyse PEM ne semble impacter que très peu les performances globales d’électrolyse par rapport à la dégradation des collecteurs de courant. / This thesis focuses on the study and the development of iridium-based electrocatalysts for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers. This work investigates in particular electrocatalyst degradation phenomena and aims at reaching an optimal OER activity-stability ratio. Various electrocatalysts (supported on high-surface area carbon, supported on doped-metal oxides and unsupported) have been synthetized and characterized by electrochemical and physico-chemical methods such as X-ray photoelectron spectroscopy, identical-location transmission electron microscopy and inductively coupled plasma mass spectrometry. Supported electrocatalysts feature stability limitations in OER conditions as revealed by agglomeration, coalescence, dissolution, and detachment of iridium oxide nanoparticles, these last two degradation mechanisms being amplified by corrosion of the carbon supports and dissolution of the elements composing the doped metal oxide supports. Unsupported electrocatalysts currently represent the best compromise between OER activity and stability. Ir(III) and Ir(V) oxides were shown to be the most active towards the OER while Ir(IV) oxide is the most stable, the least stable species being metallic iridium Ir(0). In real PEM water electrolyzers, the global electrolysis performance seems to be less impacted by the degradation of catalytic layers than the degradation of current collectors.

Thesis: Ph. D., Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Tracing the evolution of Earth's redox history is one of the great challenges of geobiology and geochemistry. The accumulation of photosynthetically derived oxygen transformed the redox state of Earth's surface environments, setting the stage for the subsequent evolution of complex life. However, the timing of the advent of oxygenic photosynthesis relative to the Great Oxidation Event (GOE; -2.4 Ga) is poorly constrained. After the deep ocean became oxygenated in the early Phanerozoic, hydrogen sulfide, which is toxic to most aerobes, may have transiently accumulated in the marine photic zone (i.e. photic zone euxinia; PZE) during mass extinctions and oceanic anoxic events. Here, the molecular fossil evidence for oxygenic photosynthesis and eukaryotes is reevaluated, where the results imply that currently existing lipid biomarkers are contaminants. Next, the stratigraphic distribution of green and purple sulfur bacteria biomarkers through geologic time is evaluated to test whether these compounds reflect a water column sulfide signal, which is implicit in their utility as PZE paleoredox proxies. Results from a modern case study underscore the need to consider allochthonous and microbial mat sources and the role of basin restriction as alternative explanations for these biomarkers in the geologic record, in addition to an autochthonous planktonic source. / by Katherine L. French. / Ph. D.

We are facing an energy crisis because of the limitation of the fossil fuel and the pollution caused by burning it. Clean energy technologies, such as fuel cells and metal-air batteries, are studied extensively because of this high efficiency and less pollution. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential in the process of energy storage and conversion, and noble metals (e.g. Pt) are needed to catalyze the critical chemical reactions in these devices. Functionalized carbon nanomaterials such as heteroatom-doped and molecule-adsorbed graphene can be used as metal-free catalysts to replace the expensive and scarce platinum-based catalysts for the energy storage and conversion. Traditionally, experimental studies on the catalytic performance of carbon nanomaterials have been conducted extensively, however, there is a lack of computational studies to guide the experiments for rapid search for the best catalysts. In addition, theoretical mechanism and the rational design principle towards ORR and OER also need to be fully understood. In this dissertation, density functional theory calculations are performed to calculate the thermodynamic and electrochemical properties of heteroatom-doped graphene and molecule-adsorbed graphene for ORR and OER. Gibb's free energy, overpotential, charge transfer and edge effect are evaluated. The charge transfer analysis show the positive charges on the graphene surface caused by the heteroatom, hetero-edges and the adsorbed organic molecules play an essential role in improving the electrochemical properties of the carbon nanomaterials. Based on the calculations, design principles are introduced to rationally design and predict the electrochemical properties of doped graphene and molecule-adsorbed graphene as metal-free catalysts for ORR and OER. An intrinsic descriptor is discovered for the first time, which can be used as a materials parameter for rational design of the metal-free catalysts with carbon nanomaterials for energy storage and conversion. The success of the design principle provides a better understanding of the mechanism behind ORR and OER and a screening approach for the best catalyst for energy storage and conversion.

Increasing energy consumption and its environmental impacts make it necessary to look for alternative energy sources. Solar energy as huge energy source which is able to cover the terms sustainability is considered as a favorable alternative. Solar cells and solar fuels are two kinds of technologies, which make us able to harness solar energy and convert it to electricity and/or store it chemically. Metal oxide semiconductors (MOSs) have a major role in these devices and optimization of their properties (composition, morphology, dimensions, crystal structure) makes it possible to increase the performance of the devices. The light absorption, charge carriers mobility, the time scale between charge injection, regeneration and recombination processes are some of the properties critical to exploitation of MOSs in solar cells and solar fuel technology. In this thesis, we explore two different systems. The first one is a NiO mesoporous semiconductor photocathode sensitized with a biomimetic Fe-Fe catalyst and a coumarin C343 dye, which was tested in a solar fuel device to produce hydrogen. This system is the first solar fuel device based on a biomimetic Fe-Fe catalyst and it shows a Faradic efficiency of 50% in hydrogen production. Cobalt catalysts have higher Faradic efficiency but their performance due to hydrolysis in low pH condition is limited. The second one is a photoanode based on the nanostructured hematite/magnetite film, which was tested in a photoelectrochemical cell. This hybrid electrode improved the photoactivity of the photoelectrochemical cell for water splitting. The main mechanism for the improvement of the functional properties relies with the role of the magnetite phase, which improves the charge carrier mobility of the composite system, compared to pure hematite, which acts as good light absorber semiconductor. By optimizing the charge separation and mobility of charge carriers of MOSs, they can be a promising active material in solar cells and solar fuel devices due to their abundance, stability, non-toxicity, and low-cost. The future work will be focused on the use of nanostructured MOSs in all-oxide solar cell devices. We have already obtained some preliminary results on 1-dimensional heterojunctions, which we report in Chapter 3.3. While they are not conclusive, they give an idea about the future direction of the present research.

Nesta tese de doutorado foram desenvolvidos e caracterizados nanomateriais eletroativos, explorando estratégias de estabilização e os efeitos sinérgicos em nanomateriais multifuncionais baseados em alfa-hidróxido de níquel, com potencial aplicação nas mais essências e urgentes áreas de atuação científica e tecnológicas, como por exemplo na conversão e armazenamento de energia, e sensores amperométricos. Nesse sentido, foram desenvolvidos nanopartículas (NPs) de alfa-hidróxidos de níquel (α-Ni(OH)2) estabilizados pela formação de nanocompósitos com óxido de grafeno (GO), denominados de α-Ni(OH)2@GO. Analogamente, foram preparados NPs de sais de hidróxido duplo de níquel e cobalto (α- NiCo(OH)2), estabilizados pela incorporação cátions Co2+ na estrutura do α-Ni(OH)2, e o correspondente nanocompósito com óxido de grafeno reduzido (rGO) denominado de α- NiCo(OH)2@rGO. De modo geral, os nanocompósitos exibiram alta capacidade de carga em elevadas densidades de corrente, alta capacidade de retenção de carga e elevada estabilidade como consequência da interação sinergística de seus componentes, com potencial aplicação em dispositivos de armazenamento de energia de alto desempenho, como por exemplo em supercapacitores híbridos. Por outro lado, um dos principais desafios no campo da conversão de energia, concentra-se no desenvolvimento de eletrocatalisadores eficientes e robustos para impulsionar a cinética intrinsecamente lenta da reação de evolução de oxigênio (OER), que envolve etapas de transferência de elétrons acopladas a de prótons. Para isso, foram preparados nanocompósitos ternários baseados em NPs de αNi(OH)2 de diferentes tamanhos, octacarboxiftalocianina de ferro (FeOCPc) e rGO (α-NiFeOCPc@rGO). As NPs de α- Ni@rGO-K maiores e mais cristalinas e seus respectivos nanocompósitos mostraram propriedades eletrocatalíticas superiores para a OER quando comparados com os respectivos derivados de α-Ni(OH)2-Na, indicando a relevância do tamanho do nanocristal de α-Ni(OH)2 na estrutura do nanocompósito e consequente efeitos sinérgicos nas propriedades eletroquímicas e eletrocatalíticas dos nanocompósitos ternários. Além disso, foram desenvolvidos eletrodos modificados com NPs de hidróxido duplo lamelar de NiCe (α-NiCe) como sensores de alta sensibilidade, e de fundamental importância para detecção e quantificação de prednisona, uma droga proibida pelo Comitê Olímpico Internacional (COI). Em resumo, a incorporação de 20% em mols de íons Ce(III/IV) em nanopartículas de α- Ni(OH)2 aumentou a estabilidade deste material na fase alfa, conferindo melhores propriedades eletrocatalíticas responsáveis pela rápida oxidação da prednisona e de seus subprodutos de degradação, permitindo a preparação de sensores amperométricos com elevada sensibilidade e baixo limite de detecção (LOD) em comparação aos eletrodos modificados já reportando na literatura. Em suma, as estratégias no design de nanomateriais foram exploradas com sucesso para gerar novos nanomateriais e nanocompósitos com propriedades eletrocatalíticas e de armazenamento de carga aprimoradas, com potencial de aplicação em sensores e supercapacitores híbridos. / In this doctoral thesis, nanomaterials design strategies were explored in order to improve the stability of alpha-nickel hydroxide nanoparticles while developing synergistic effects, generating multifunctional electrochemically active nanomaterials and nanocomposites with potential application in amperometric sensors and energy conversion and storage devices. In this context, the α-Ni(OH)2 NPs were stabilized by generating double hydroxide salts, by interaction with octacarboxyphthalocyanine molecules and graphene oxide (GO) generating hybrid and nanocomposite materials, for example α-Ni(OH)2@GO. Nickel hydroxide NPs was stabilized by incorporation of Co2+ cation to produce α-NixCoy(OH)2 double hydroxide salts and the corresponding nanocomposite with reduced graphene oxide (rGO) designated - NiCo(OH)2@rGO. In this way, nanocomposites with potential application in high performance energy storage devices such as hybrid supercapacitors were produced, since exhibited large charge capacities at high current densities and great stability as a consequence of the synergistic interaction of their componentes. One of the main challenges in the field of energy conversion, the development of efficient and robust electrocatalysts to boost the intrinsically slow multielectronic multiprotonic transfer kinetics of the oxygen evolution reaction (OER) was also addressed using ternary nanocomposites based on α-Ni(OH)2 NPs, iron octacarboxyphthalocyanine (FeOCPc) and rGO (α-NiFeOCPc@rGO). The more crystalline - Ni@rGO-K NPs and their respective nanocomposites showed superior electrocatalytic properties when compared to the respective α-Ni(OH)2-Na derivatives, indicating the relevance of the α-Ni(OH)2 nanocrystal size and synergistic effects on their electrochemical and electrocatalytic properties. In addition, amperometric sensors based on NiCe layered doublehydroxide NPs (α-NiCe) were developed for determination of prednisone, a drug forbidden by the International Olympic Committee (IOC). The incorporation of 20 m% of Ce3+/4+ ions in α- Ni(OH)2 nanoparticles increased its stability in the alpha phase, conferring improved electrocatalytic properties responsible for the rapid oxidation of prednisone and its degradation byproducts, responsible for the higher sensitivity and lower detection limits (LOD) than similar devices reported in the literature. In short, nanomaterials design strategies were successfully explored to generated new nanomaterials and nanocomposites with enhanced electrocatalytic and charge storage properties with potential application in sensors and hybrid supercapacitors.

O dióxido de manganês (MnO2) é um catalisador eficiente de baixo custo utilizado no cátodo de baterias do tipo metal-ar e células a combustível alcalinas, sendo capaz de promover a redução completa de oxigênio pela rota 4e-. No entanto, o dióxido de manganês é um semicondutor e só pode ser utilizado como material eletródico nos dispositivos mencionados se combinado com algum suporte condutor. O suporte condutor mais utilizado para este fim é o carbono em pó. Entretanto, este material não possui estabilidade suficiente nas condições operacionais das células alcalinas, sendo convertido gradativamente em CO2. Uma das possíveis estratégias para tentar minimizar esta deficiência é incrementar a condutividade eletrônica do óxido puro pela dopagem com alguns cátions metálicos. Sendo assim, este trabalho tem como objetivo geral pesquisar de maneira sistemática o efeito da dopagem de dióxido de manganês com alguns cátions metálicos, como o Bi3+e Ce4+ nas propriedades físico-químicas e eletrocatalíticas deste óxido, visando o uso dos mesmos como em cátodos de baterias recarregáveis do tipo Zn-ar. As análises das características morfológicas dos catalisadores por meio de MEV e TEM mostram que os óxidos de manganês são gerados na forma de nano-bastões de 50 a 100 nm de comprimento. Os óxidos puros e dopados com bismuto e cério apresentam estruturas tetragonais típicas, ocorrendo expansão da célula unitária dos óxidos dopados pela troca de íons manganês pelos correspondentes dopantes na rede cristalina de MnO2. Os resultados eletroquímicos sugerem um aumento de condutividade do óxido dopado que possibilita seu uso sem mistura com carbono. Além disso, observa-se que a RRO é catalisada por um mecanismo que envolve a transferência de 4e- nestes materiais com participação de peróxido como intermediário. O óxido de manganês dopado com Bi apresentou promissor desempenho catalítico para a RDO, o que junto com os demais resultados apresentados para a RRO o qualificou a funcionar como o catalisador bifuncional mais promissor de todos os estudados em baterias do tipo metal-ar. Experimentos realizados em mini baterias do tipo Zn-ar demonstraram a total capacidade do catalisador dopado com bismuto operar como catalisador do eletrodo de ar, resultando num desempenho superior ao de um catalisador convencional de MnO2/C. / Manganese dioxide is at the same time an efficient and low-cost material used as cathode catalyst in the air electrode of metal-air and alkaline fuel cells, capable to promote the complete reduction of oxygen thru the 4e- mechanism. However, manganese dioxide is a semiconductor and can be used as electrodic material in the mentioned devices only combined with a conductor support. High surface area carbon powder is the most commonly used material for such purpose. The problem is that carbon suffers from severe instabilities in the experimental conditions that fuel cells and metal-air batteries operates, being gradually converted into CO2. A possible strategy to overcome or at least minimize the low oxide conductivity is by doping this material with some metallic cations. In this sense, the main purpose of this work was the systematic investigation of the physicochemical and electrocatalytic properties of Bi3+ and Ce4+ doped manganese dioxide materials used as cathode catalysts in the air electrode of alkaline type Zn-air batteries. The morphologic characterization performed SEM and TEM revealed that pure as well cation doped MnO2 are formed as poly dispersed nanorods with 50-100 nm length. Both pure and doped materials presented typical tetragonal structures, although a cell expansion was observed in the doped oxides caused by the exchange of some manganese cations by the doping counter parts. Electrochemical results suggest that a material with increased conductivity results from the doping process, allowing it to operate as air catalyst without the use of a carbon support. Besides, it is observed that the oxygen reduction reaction proceeds thru the 4e- mechanism on the doped oxides involving hydrogen peroxide as intermediate. The Bi doped oxide presented the best performance for the oxygen evolution reaction among all catalysts investigated. This result together with the superior performance for the oxygen reduction reaction presented by this material suggest that Bi doped MnO2 is a potential candidate to operate as an air catalyst of rechargeable alkaline metal-air batteries. Experiments conducted in a mini Zn-air battery using Bi doped MnO2 as air catalyst corroborated this observation.

O dióxido de manganês (MnO2) é um catalisador eficiente de baixo custo utilizado no cátodo de baterias do tipo metal-ar e células a combustível alcalinas, sendo capaz de promover a redução completa de oxigênio pela rota 4e-. No entanto, o dióxido de manganês é um semicondutor e só pode ser utilizado como material eletródico nos dispositivos mencionados se combinado com algum suporte condutor. O suporte condutor mais utilizado para este fim é o carbono em pó. Entretanto, este material não possui estabilidade suficiente nas condições operacionais das células alcalinas, sendo convertido gradativamente em CO2. Uma das possíveis estratégias para tentar minimizar esta deficiência é incrementar a condutividade eletrônica do óxido puro pela dopagem com alguns cátions metálicos. Sendo assim, este trabalho tem como objetivo geral pesquisar de maneira sistemática o efeito da dopagem de dióxido de manganês com alguns cátions metálicos, como o Bi3+e Ce4+ nas propriedades físico-químicas e eletrocatalíticas deste óxido, visando o uso dos mesmos como em cátodos de baterias recarregáveis do tipo Zn-ar. As análises das características morfológicas dos catalisadores por meio de MEV e TEM mostram que os óxidos de manganês são gerados na forma de nano-bastões de 50 a 100 nm de comprimento. Os óxidos puros e dopados com bismuto e cério apresentam estruturas tetragonais típicas, ocorrendo expansão da célula unitária dos óxidos dopados pela troca de íons manganês pelos correspondentes dopantes na rede cristalina de MnO2. Os resultados eletroquímicos sugerem um aumento de condutividade do óxido dopado que possibilita seu uso sem mistura com carbono. Além disso, observa-se que a RRO é catalisada por um mecanismo que envolve a transferência de 4e- nestes materiais com participação de peróxido como intermediário. O óxido de manganês dopado com Bi apresentou promissor desempenho catalítico para a RDO, o que junto com os demais resultados apresentados para a RRO o qualificou a funcionar como o catalisador bifuncional mais promissor de todos os estudados em baterias do tipo metal-ar. Experimentos realizados em mini baterias do tipo Zn-ar demonstraram a total capacidade do catalisador dopado com bismuto operar como catalisador do eletrodo de ar, resultando num desempenho superior ao de um catalisador convencional de MnO2/C. / Manganese dioxide is at the same time an efficient and low-cost material used as cathode catalyst in the air electrode of metal-air and alkaline fuel cells, capable to promote the complete reduction of oxygen thru the 4e- mechanism. However, manganese dioxide is a semiconductor and can be used as electrodic material in the mentioned devices only combined with a conductor support. High surface area carbon powder is the most commonly used material for such purpose. The problem is that carbon suffers from severe instabilities in the experimental conditions that fuel cells and metal-air batteries operates, being gradually converted into CO2. A possible strategy to overcome or at least minimize the low oxide conductivity is by doping this material with some metallic cations. In this sense, the main purpose of this work was the systematic investigation of the physicochemical and electrocatalytic properties of Bi3+ and Ce4+ doped manganese dioxide materials used as cathode catalysts in the air electrode of alkaline type Zn-air batteries. The morphologic characterization performed SEM and TEM revealed that pure as well cation doped MnO2 are formed as poly dispersed nanorods with 50-100 nm length. Both pure and doped materials presented typical tetragonal structures, although a cell expansion was observed in the doped oxides caused by the exchange of some manganese cations by the doping counter parts. Electrochemical results suggest that a material with increased conductivity results from the doping process, allowing it to operate as air catalyst without the use of a carbon support. Besides, it is observed that the oxygen reduction reaction proceeds thru the 4e- mechanism on the doped oxides involving hydrogen peroxide as intermediate. The Bi doped oxide presented the best performance for the oxygen evolution reaction among all catalysts investigated. This result together with the superior performance for the oxygen reduction reaction presented by this material suggest that Bi doped MnO2 is a potential candidate to operate as an air catalyst of rechargeable alkaline metal-air batteries. Experiments conducted in a mini Zn-air battery using Bi doped MnO2 as air catalyst corroborated this observation.

<p>A molecular system capable of photoinduced water splitting is an attractive approach to solar energy conversion. This thesis deals with the functional characterization of molecular building blocks for the three principal functions of such a molecular system: Photoinduced accumulative charge separation, catalytic water oxidation, and catalytic proton reduction. </p><p>Systems combining a ruthenium-trisbipyridine photosensitizer with multi-electron donors in form of dinuclear ruthenium or manganese complexes were investigated in view of the rate constants of electron transfer and excited state quenching. The kinetics were studied in the different oxidation states of the donor unit by combination of electrochemistry and time resolved spectroscopy. The rapid excited state quenching by the multi-electron donors points to the importance of redox intermediates for efficient accumulative photooxidation of the terminal donor.</p><p>The redox behavior of manganese complexes as mimics of the water oxidizing catalyst in the natural photosynthetic reaction center was studied by electrochemical and spectroscopic methods. For a dinuclear manganese complex ligand exchange reactions were studied in view of their importance for the accumulative oxidation of the complex and its reactivity towards water. With the binding of substrate water, multiple oxidation in a narrow potential range and concomitant deprotonation of the bound water it was demonstrated that the manganese complex is capable of mimicking multiple aspects of photosynthetic water oxidation.</p><p>A dinuclear iron complex was investigated as biomimetic proton reduction catalyst. The complex structurally mimics the active site of the iron-only hydrogenase enzyme and was designed to hold a proton on the bridging ligand and a hydride on the iron centers. Thermodynamics and kinetics of the protonation reactions and the electrochemical behavior of the different protonation states were studied in view of their potential catalytic performance.</p>

A molecular system capable of photoinduced water splitting is an attractive approach to solar energy conversion. This thesis deals with the functional characterization of molecular building blocks for the three principal functions of such a molecular system: Photoinduced accumulative charge separation, catalytic water oxidation, and catalytic proton reduction. Systems combining a ruthenium-trisbipyridine photosensitizer with multi-electron donors in form of dinuclear ruthenium or manganese complexes were investigated in view of the rate constants of electron transfer and excited state quenching. The kinetics were studied in the different oxidation states of the donor unit by combination of electrochemistry and time resolved spectroscopy. The rapid excited state quenching by the multi-electron donors points to the importance of redox intermediates for efficient accumulative photooxidation of the terminal donor. The redox behavior of manganese complexes as mimics of the water oxidizing catalyst in the natural photosynthetic reaction center was studied by electrochemical and spectroscopic methods. For a dinuclear manganese complex ligand exchange reactions were studied in view of their importance for the accumulative oxidation of the complex and its reactivity towards water. With the binding of substrate water, multiple oxidation in a narrow potential range and concomitant deprotonation of the bound water it was demonstrated that the manganese complex is capable of mimicking multiple aspects of photosynthetic water oxidation. A dinuclear iron complex was investigated as biomimetic proton reduction catalyst. The complex structurally mimics the active site of the iron-only hydrogenase enzyme and was designed to hold a proton on the bridging ligand and a hydride on the iron centers. Thermodynamics and kinetics of the protonation reactions and the electrochemical behavior of the different protonation states were studied in view of their potential catalytic performance.

The Arbuscular mycorrhiza (AM) is an endosymbiont of higher plant roots. Most land plants and cultivated crops are concerned to AM symbiosis. This endosymbiosis is based on the mutual exchange of nutrients between plant and fungus. Therefore, AM symbiosis leads to an increased demand for photosynthetic products. The aim of this study was to investigate the pathway used by plants during AM symbiosis to increase photosynthetic performance. Therefore, we have carried out a systematic characterization of photosynthesis in Medicago truncatula (M. truncatula), which is a model legume. We observed colonization by the fungus in roots and that AM symbiosis increases the fresh and dry plant biomass. This could be attributed to an increase in both photosynthetic efficiency and capacity in AM plants. Consistent with these observations, AM symbiosis enhanced phosphorus uptake from the soil into roots, stems and leaves, as based on analyses of phosphorus content. Based on equal chl loading, no differences were found regarding D1, Lhcb1 and Lhcb2 protein content in four plant groups. This indicates similar ratio between chl and PSII proteins. Furthermore, AM symbiosis increases the amount of chlorophyll, steady state oxygen evolution activities, maximum quantum yield (Fv/Fm), and photosynthetic electron transport rate (about 5 fold). Nevertheless, photoprotection was not affected by AM symbiosis. We observed an increase in weight of seed/fruit and weight of seed/plant in AM plants (about 2 fold). Based on these results, we propose that AM symbiosis increases both the efficiency and the capacity of photosynthetic apparatus in the M. truncatula.